From 53ec2eff77b54c5dfe2f00a76cce5e1bffbc0e9f Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Wed, 4 Jul 2018 14:57:36 -0400
Subject: [PATCH 01/27] Add support for static_path resources.

---
 dash/resources.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/dash/resources.py b/dash/resources.py
index c08c0bad3f..e6cb2dc5ab 100644
--- a/dash/resources.py
+++ b/dash/resources.py
@@ -30,6 +30,8 @@ def _filter_resources(self, all_resources):
                 )
             elif 'absolute_path' in s:
                 filtered_resource['absolute_path'] = s['absolute_path']
+            elif 'static_path' in s:
+                filtered_resource = s
             elif self.config.serve_locally:
                 warnings.warn(
                     'A local version of {} is not available'.format(

From a14709a4bb24432adcebe65d0b4175d5a36e9051 Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Wed, 4 Jul 2018 15:29:13 -0400
Subject: [PATCH 02/27] Add static directory walk for files to include.

---
 dash/dash.py | 68 ++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 58 insertions(+), 10 deletions(-)

diff --git a/dash/dash.py b/dash/dash.py
index 143d1e802b..fc470ebb33 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -1,5 +1,6 @@
 from __future__ import print_function
 
+import os
 import sys
 import collections
 import importlib
@@ -28,7 +29,9 @@ def __init__(
             self,
             name='__main__',
             server=None,
-            static_folder='static',
+            static_folder=None,
+            static_url_path='/static',
+            include_static_files=True,
             url_base_pathname='/',
             compress=True,
             **kwargs):
@@ -43,14 +46,36 @@ def __init__(
                 ''', DeprecationWarning)
 
         name = name or 'dash'
+
+        lib_dir = os.path.abspath(
+            os.path.join(os.path.dirname(__file__), '..'))
+        template_folder = os.path.join(lib_dir, 'templates')
+        lib_static = os.path.join(lib_dir, 'static')
+
+        # Set the static folder (same as flask does, but we can use it)
+        static_folder = static_folder or os.path.join(
+            os.getcwd(), 'static'
+        )
+
         # allow users to supply their own flask server
-        self.server = server or Flask(name, static_folder=static_folder)
+        self.server = server or Flask(name,
+                                      static_folder=static_folder,
+                                      static_url_path=static_url_path)
+
+        _dash_files = flask.Blueprint('_dash_files',
+                                      '_dash_files',
+                                      url_prefix='/dash-files',
+                                      static_folder=lib_static,
+                                      template_folder=template_folder)
+
+        self.server.register_blueprint(_dash_files)
 
         self.url_base_pathname = url_base_pathname
         self.config = _AttributeDict({
             'suppress_callback_exceptions': False,
             'routes_pathname_prefix': url_base_pathname,
-            'requests_pathname_prefix': url_base_pathname
+            'requests_pathname_prefix': url_base_pathname,
+            'include_static_files': True,
         })
 
         # list of dependencies
@@ -149,12 +174,6 @@ def layout(self, value):
         # pylint: disable=protected-access
         self.css._update_layout(layout_value)
         self.scripts._update_layout(layout_value)
-        self._collect_and_register_resources(
-            self.scripts.get_all_scripts()
-        )
-        self._collect_and_register_resources(
-            self.css.get_all_css()
-        )
 
     def serve_layout(self):
         layout = self._layout_value()
@@ -180,6 +199,7 @@ def serve_routes(self):
         )
 
     def _collect_and_register_resources(self, resources):
+        # now needs the app context.
         # template in the necessary component suite JS bundles
         # add the version number of the package as a query parameter
         # for cache busting
@@ -217,8 +237,12 @@ def _relative_url_path(relative_package_path='', namespace=''):
                         srcs.append(url)
             elif 'absolute_path' in resource:
                 raise Exception(
-                    'Serving files form absolute_path isn\'t supported yet'
+                    'Serving files from absolute_path isn\'t supported yet'
                 )
+            elif 'static_path' in resource:
+                static_url = flask.url_for('static',
+                                           filename=resource['static_path'])
+                srcs.append(static_url)
         return srcs
 
     def _generate_css_dist_html(self):
@@ -558,9 +582,33 @@ def dispatch(self):
         return self.callback_map[target_id]['callback'](*args)
 
     def _setup_server(self):
+        if self.config.include_static_files:
+            self._walk_static_directory()
+
         self._generate_scripts_html()
         self._generate_css_dist_html()
 
+    def _walk_static_directory(self):
+        walk_dir = self.config.static_folder
+        subs = []
+        for current, _, files in os.walk(walk_dir):
+            if current != walk_dir:
+                subs.append(os.path.basename(current))
+
+            for f in files:
+
+                # path.join is bad here cause we call url_for
+                path = f if not subs else '/'.join(subs + [f])
+
+                if f.endswith('js'):
+                    self.scripts.append_script({
+                        'static_path': path
+                    })
+                elif f.endswith('css'):
+                    self.css.append_css({
+                        'static_path': path
+                    })
+
     def run_server(self,
                    port=8050,
                    debug=False,

From 69b8adc9718529372805e287767e93ba7545adca Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Wed, 4 Jul 2018 15:52:53 -0400
Subject: [PATCH 03/27] pylint fixes.

---
 dash/dash.py      | 2 +-
 dash/resources.py | 4 +---
 2 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/dash/dash.py b/dash/dash.py
index fc470ebb33..43716a98e3 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -23,7 +23,7 @@
 
 
 # pylint: disable=too-many-instance-attributes
-# pylint: disable=too-many-arguments
+# pylint: disable=too-many-arguments, too-many-locals
 class Dash(object):
     def __init__(
             self,
diff --git a/dash/resources.py b/dash/resources.py
index e6cb2dc5ab..b4f61bc075 100644
--- a/dash/resources.py
+++ b/dash/resources.py
@@ -21,7 +21,6 @@ def _filter_resources(self, all_resources):
             filtered_resource = {}
             if 'namespace' in s:
                 filtered_resource['namespace'] = s['namespace']
-
             if 'external_url' in s and not self.config.serve_locally:
                 filtered_resource['external_url'] = s['external_url']
             elif 'relative_package_path' in s:
@@ -114,8 +113,7 @@ class config:
         serve_locally = False
 
 
-class Scripts:
-    # pylint: disable=old-style-class
+class Scripts:  # pylint: disable=old-style-class
     def __init__(self, layout=None):
         self._resources = Resources('_js_dist', layout)
         self._resources.config = self.config

From 7cafb47b0f5e38128530a96463d4719041cf4622 Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Wed, 4 Jul 2018 16:16:06 -0400
Subject: [PATCH 04/27] Add support for meta tags.

---
 dash/dash.py | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/dash/dash.py b/dash/dash.py
index 43716a98e3..96f6435cf5 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -75,12 +75,14 @@ def __init__(
             'suppress_callback_exceptions': False,
             'routes_pathname_prefix': url_base_pathname,
             'requests_pathname_prefix': url_base_pathname,
-            'include_static_files': True,
+            'include_static_files': include_static_files,
         })
 
         # list of dependencies
         self.callback_map = {}
 
+        self._meta_tags = collections.OrderedDict()
+
         if compress:
             # gzip
             Compress(self.server)
@@ -318,6 +320,7 @@ def index(self, *args, **kwargs):  # pylint: disable=unused-argument
         scripts = self._generate_scripts_html()
         css = self._generate_css_dist_html()
         config = self._generate_config_html()
+        metas = self._meta_tags.values()
         title = getattr(self, 'title', 'Dash')
         return '''
         <!DOCTYPE html>
@@ -609,6 +612,9 @@ def _walk_static_directory(self):
                         'static_path': path
                     })
 
+    def add_meta_tag(self, name, content):
+        self._meta_tags[name] = {'name': name, 'content': content}
+
     def run_server(self,
                    port=8050,
                    debug=False,

From 7ebab390b2ada25209b35757d4fbd936ec927c84 Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Wed, 4 Jul 2018 17:48:43 -0400
Subject: [PATCH 05/27] Add support favicon located in static dir.

---
 dash/dash.py | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/dash/dash.py b/dash/dash.py
index 96f6435cf5..21eb119feb 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -76,12 +76,14 @@ def __init__(
             'routes_pathname_prefix': url_base_pathname,
             'requests_pathname_prefix': url_base_pathname,
             'include_static_files': include_static_files,
+            'static_folder': static_folder
         })
 
         # list of dependencies
         self.callback_map = {}
 
         self._meta_tags = collections.OrderedDict()
+        self._favicon = None
 
         if compress:
             # gzip
@@ -611,6 +613,8 @@ def _walk_static_directory(self):
                     self.css.append_css({
                         'static_path': path
                     })
+                elif f == 'favicon.ico':
+                    self._favicon = path
 
     def add_meta_tag(self, name, content):
         self._meta_tags[name] = {'name': name, 'content': content}

From fc265442e067057cd84202032e5d0bd5f586703e Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Thu, 5 Jul 2018 17:49:40 -0400
Subject: [PATCH 06/27] Fix static walking nested directories.

---
 dash/dash.py | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/dash/dash.py b/dash/dash.py
index 21eb119feb..c4712c8be5 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -7,6 +7,9 @@
 import json
 import pkgutil
 import warnings
+import shutil
+import re
+
 from functools import wraps
 
 import plotly
@@ -595,15 +598,24 @@ def _setup_server(self):
 
     def _walk_static_directory(self):
         walk_dir = self.config.static_folder
-        subs = []
+        slash_splitter = re.compile(r'[\\/]+')
+
         for current, _, files in os.walk(walk_dir):
-            if current != walk_dir:
-                subs.append(os.path.basename(current))
+            if current == walk_dir:
+                base = ''
+            else:
+                s = current.replace(walk_dir, '').lstrip('\\').lstrip('/')
+                splitted = slash_splitter.split(s)
+                if len(splitted) > 1:
+                    base = '/'.join(slash_splitter.split(s))
+                else:
+                    base = splitted[0]
 
             for f in files:
-
-                # path.join is bad here cause we call url_for
-                path = f if not subs else '/'.join(subs + [f])
+                if base:
+                    path = '/'.join([base, f])
+                else:
+                    path = f
 
                 if f.endswith('js'):
                     self.scripts.append_script({

From d2cce95a12badafb497785c0663495a329f66f13 Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Fri, 6 Jul 2018 15:16:57 -0400
Subject: [PATCH 07/27] Changed the meta tags dict to a list, added meta_tags
 to dash.__init__.

---
 dash/dash.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/dash/dash.py b/dash/dash.py
index c4712c8be5..d6e5f41472 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -37,6 +37,7 @@ def __init__(
             include_static_files=True,
             url_base_pathname='/',
             compress=True,
+            meta_tags=None,
             **kwargs):
 
         # pylint-disable: too-many-instance-attributes
@@ -85,7 +86,7 @@ def __init__(
         # list of dependencies
         self.callback_map = {}
 
-        self._meta_tags = collections.OrderedDict()
+        self._meta_tags = meta_tags or []
         self._favicon = None
 
         if compress:
@@ -629,7 +630,7 @@ def _walk_static_directory(self):
                     self._favicon = path
 
     def add_meta_tag(self, name, content):
-        self._meta_tags[name] = {'name': name, 'content': content}
+        self._meta_tags.append({'name': name, 'content': content})
 
     def run_server(self,
                    port=8050,

From 1212ee53b50b6e9e839b728ff953fcb563436b0a Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Fri, 6 Jul 2018 16:41:53 -0400
Subject: [PATCH 08/27] Add test for meta tags.

---
 tests/test_integration.py | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/tests/test_integration.py b/tests/test_integration.py
index 1bdc298c41..25ec3c19da 100644
--- a/tests/test_integration.py
+++ b/tests/test_integration.py
@@ -266,3 +266,30 @@ def display_output(react_value, flow_value):
         self.startServer(app)
         self.wait_for_element_by_id('waitfor')
         self.percy_snapshot(name='flowtype')
+
+    def test_meta_tags(self):
+        app = dash.Dash()
+
+        app.layout = html.Div(id='content')
+
+        metas = (
+            ('description', 'my dash app'),
+            ('custom', 'customized')
+        )
+
+        for m in metas:
+            app.add_meta_tag(*m)
+
+        self.startServer(app)
+
+        meta = self.driver.find_elements_by_tag_name('meta')
+
+        self.assertEqual(len(metas), len(meta) - 1, 'Not enough meta tags')
+
+        for i in range(1, len(meta)):
+            meta_tag = meta[i]
+            meta_info = metas[i - 1]
+            name = meta_tag.get_attribute('name')
+            content = meta_tag.get_attribute('content')
+            self.assertEqual(name, meta_info[0])
+            self.assertEqual(content, meta_info[1])

From 846c8fcf3250649809eadc065857071f97ef268e Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Tue, 10 Jul 2018 12:14:01 -0400
Subject: [PATCH 09/27] Fix bad line that was included in rebase.

---
 dash/dash.py | 2 --
 1 file changed, 2 deletions(-)

diff --git a/dash/dash.py b/dash/dash.py
index d6e5f41472..df748d7a62 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -7,7 +7,6 @@
 import json
 import pkgutil
 import warnings
-import shutil
 import re
 
 from functools import wraps
@@ -326,7 +325,6 @@ def index(self, *args, **kwargs):  # pylint: disable=unused-argument
         scripts = self._generate_scripts_html()
         css = self._generate_css_dist_html()
         config = self._generate_config_html()
-        metas = self._meta_tags.values()
         title = getattr(self, 'title', 'Dash')
         return '''
         <!DOCTYPE html>

From 4777731bdae3a26de0a3ecea54194b0982ba1a91 Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Tue, 10 Jul 2018 12:21:33 -0400
Subject: [PATCH 10/27] Add support for static external resources.

---
 dash/dash.py      | 18 +++++++++++-------
 dash/resources.py |  2 +-
 2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/dash/dash.py b/dash/dash.py
index df748d7a62..daec47a51e 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -79,7 +79,8 @@ def __init__(
             'routes_pathname_prefix': url_base_pathname,
             'requests_pathname_prefix': url_base_pathname,
             'include_static_files': include_static_files,
-            'static_folder': static_folder
+            'static_folder': static_folder,
+            'static_external_path': ''
         })
 
         # list of dependencies
@@ -599,6 +600,13 @@ def _walk_static_directory(self):
         walk_dir = self.config.static_folder
         slash_splitter = re.compile(r'[\\/]+')
 
+        def add_resource(p):
+            res = {'static_path': p}
+            if self.config.static_external_path:
+                res['external_url'] = '{}{}'.format(
+                    self.config.static_external_path, path)
+            return res
+
         for current, _, files in os.walk(walk_dir):
             if current == walk_dir:
                 base = ''
@@ -617,13 +625,9 @@ def _walk_static_directory(self):
                     path = f
 
                 if f.endswith('js'):
-                    self.scripts.append_script({
-                        'static_path': path
-                    })
+                    self.scripts.append_script(add_resource(path))
                 elif f.endswith('css'):
-                    self.css.append_css({
-                        'static_path': path
-                    })
+                    self.css.append_css(add_resource(path))
                 elif f == 'favicon.ico':
                     self._favicon = path
 
diff --git a/dash/resources.py b/dash/resources.py
index b4f61bc075..9ee82e4f7d 100644
--- a/dash/resources.py
+++ b/dash/resources.py
@@ -30,7 +30,7 @@ def _filter_resources(self, all_resources):
             elif 'absolute_path' in s:
                 filtered_resource['absolute_path'] = s['absolute_path']
             elif 'static_path' in s:
-                filtered_resource = s
+                filtered_resource['static_path'] = s['static_path']
             elif self.config.serve_locally:
                 warnings.warn(
                     'A local version of {} is not available'.format(

From 23195f0e5e0bd157a8a3a88fa6eb5bfd16ec2c63 Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Tue, 10 Jul 2018 12:31:10 -0400
Subject: [PATCH 11/27] Rename `static` to `assets` for user static file
 includes.

---
 dash/dash.py      | 60 ++++++++++++++++++++---------------------------
 dash/resources.py |  4 ++--
 2 files changed, 27 insertions(+), 37 deletions(-)

diff --git a/dash/dash.py b/dash/dash.py
index daec47a51e..dc5daba7c0 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -31,9 +31,9 @@ def __init__(
             self,
             name='__main__',
             server=None,
-            static_folder=None,
-            static_url_path='/static',
-            include_static_files=True,
+            assets_folder=None,
+            assets_url_path='/assets',
+            include_assets_files=True,
             url_base_pathname='/',
             compress=True,
             meta_tags=None,
@@ -50,37 +50,23 @@ def __init__(
 
         name = name or 'dash'
 
-        lib_dir = os.path.abspath(
-            os.path.join(os.path.dirname(__file__), '..'))
-        template_folder = os.path.join(lib_dir, 'templates')
-        lib_static = os.path.join(lib_dir, 'static')
-
-        # Set the static folder (same as flask does, but we can use it)
-        static_folder = static_folder or os.path.join(
-            os.getcwd(), 'static'
+        self.assets_folder = assets_folder or os.path.join(
+            os.getcwd(), 'assets'
         )
 
         # allow users to supply their own flask server
-        self.server = server or Flask(name,
-                                      static_folder=static_folder,
-                                      static_url_path=static_url_path)
-
-        _dash_files = flask.Blueprint('_dash_files',
-                                      '_dash_files',
-                                      url_prefix='/dash-files',
-                                      static_folder=lib_static,
-                                      template_folder=template_folder)
-
-        self.server.register_blueprint(_dash_files)
+        self.server = server or Flask(name)
 
         self.url_base_pathname = url_base_pathname
         self.config = _AttributeDict({
             'suppress_callback_exceptions': False,
             'routes_pathname_prefix': url_base_pathname,
             'requests_pathname_prefix': url_base_pathname,
-            'include_static_files': include_static_files,
-            'static_folder': static_folder,
-            'static_external_path': ''
+            'include_assets_files': include_assets_files,
+            'assets_folder': assets_folder or os.path.join(
+                os.getcwd(), 'assets'),
+            'assets_external_path': '',
+            'assets_url_path': assets_url_path,
         })
 
         # list of dependencies
@@ -247,9 +233,9 @@ def _relative_url_path(relative_package_path='', namespace=''):
                 raise Exception(
                     'Serving files from absolute_path isn\'t supported yet'
                 )
-            elif 'static_path' in resource:
-                static_url = flask.url_for('static',
-                                           filename=resource['static_path'])
+            elif 'asset_path' in resource:
+                static_url = flask.url_for('assets.static',
+                                           filename=resource['asset_path'])
                 srcs.append(static_url)
         return srcs
 
@@ -590,21 +576,21 @@ def dispatch(self):
         return self.callback_map[target_id]['callback'](*args)
 
     def _setup_server(self):
-        if self.config.include_static_files:
-            self._walk_static_directory()
+        if self.config.include_assets_files:
+            self._walk_assets_directory()
 
         self._generate_scripts_html()
         self._generate_css_dist_html()
 
-    def _walk_static_directory(self):
-        walk_dir = self.config.static_folder
+    def _walk_assets_directory(self):
+        walk_dir = self.config.assets_folder
         slash_splitter = re.compile(r'[\\/]+')
 
         def add_resource(p):
-            res = {'static_path': p}
-            if self.config.static_external_path:
+            res = {'asset_path': p}
+            if self.config.assets_external_path:
                 res['external_url'] = '{}{}'.format(
-                    self.config.static_external_path, path)
+                    self.config.assets_external_path, path)
             return res
 
         for current, _, files in os.walk(walk_dir):
@@ -638,4 +624,8 @@ def run_server(self,
                    port=8050,
                    debug=False,
                    **flask_run_options):
+        bp = flask.Blueprint('assets', 'assets',
+                             static_folder=self.config.assets_folder,
+                             static_url_path=self.config.assets_url_path)
+        self.server.register_blueprint(bp)
         self.server.run(port=port, debug=debug, **flask_run_options)
diff --git a/dash/resources.py b/dash/resources.py
index 9ee82e4f7d..70f37a5389 100644
--- a/dash/resources.py
+++ b/dash/resources.py
@@ -29,8 +29,8 @@ def _filter_resources(self, all_resources):
                 )
             elif 'absolute_path' in s:
                 filtered_resource['absolute_path'] = s['absolute_path']
-            elif 'static_path' in s:
-                filtered_resource['static_path'] = s['static_path']
+            elif 'asset_path' in s:
+                filtered_resource['asset_path'] = s['asset_path']
             elif self.config.serve_locally:
                 warnings.warn(
                     'A local version of {} is not available'.format(

From 0c96dc71af985de7b0d05b0e345509115b16a357 Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Tue, 10 Jul 2018 14:40:55 -0400
Subject: [PATCH 12/27] Add _generate_meta_html to build html meta tags.

---
 dash/dash.py | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/dash/dash.py b/dash/dash.py
index dc5daba7c0..f930def97e 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -278,6 +278,20 @@ def _generate_config_html(self):
             '</script>'
         ).format(json.dumps(self._config()))
 
+    def _generate_meta_html(self):
+        has_charset = any(filter(lambda x: 'charset' in x, self._meta_tags))
+
+        tags = []
+        if not has_charset:
+            tags.append('<meta charset="UTF-8"/>')
+        for meta in self._meta_tags:
+            attributes = []
+            for k, v in meta.items():
+                attributes.append('{}="{}"'.format(k, v))
+            tags.append('<meta {} />'.format(' '.join(attributes)))
+
+        return '\n      '.join(tags)
+
     # Serve the JS bundles for each package
     def serve_component_suites(self, package_name, path_in_package_dist):
         if package_name not in self.registered_paths:
@@ -312,12 +326,13 @@ def index(self, *args, **kwargs):  # pylint: disable=unused-argument
         scripts = self._generate_scripts_html()
         css = self._generate_css_dist_html()
         config = self._generate_config_html()
+        metas = self._generate_meta_html()
         title = getattr(self, 'title', 'Dash')
         return '''
         <!DOCTYPE html>
         <html>
             <head>
-                <meta charset="UTF-8">
+                {}
                 <title>{}</title>
                 {}
             </head>
@@ -333,7 +348,7 @@ def index(self, *args, **kwargs):  # pylint: disable=unused-argument
                 </footer>
             </body>
         </html>
-        '''.format(title, css, config, scripts)
+        '''.format(metas, title, css, config, scripts)
 
     def dependencies(self):
         return flask.jsonify([

From f9434716bf093d6267b233450bfa3756bcb6bd66 Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Tue, 10 Jul 2018 15:08:49 -0400
Subject: [PATCH 13/27] Add index customization by string interpolations.

---
 dash/_utils.py |  8 +++++++
 dash/dash.py   | 61 +++++++++++++++++++++++++++++++++-----------------
 2 files changed, 48 insertions(+), 21 deletions(-)

diff --git a/dash/_utils.py b/dash/_utils.py
index edc5c20f52..11d1cfd6f6 100644
--- a/dash/_utils.py
+++ b/dash/_utils.py
@@ -1,3 +1,11 @@
+def interpolate_str(template, **data):
+    s = template
+    for k, v in data.items():
+        key = '%({})'.format(k)
+        s = s.replace(key, v)
+    return s
+
+
 class AttributeDict(dict):
     """
     Dictionary subclass enabling attribute lookup/assignment of keys/values.
diff --git a/dash/dash.py b/dash/dash.py
index f930def97e..d5d947661a 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -22,6 +22,33 @@
 from .development.base_component import Component
 from . import exceptions
 from ._utils import AttributeDict as _AttributeDict
+from ._utils import interpolate_str
+
+_default_index = '''
+<!DOCTYPE html>
+<html>
+    <head>
+        %(metas)
+        <title>%(title)</title>
+        %(css)
+    </head>
+    <body>
+        %(app_entry)
+        <footer>
+            %(config)
+            %(scripts)
+        </footer>
+    </body>
+</html>
+'''
+
+_app_entry = '''
+<div id="react-entry-point">
+    <div class="_dash-loading">
+        Loading...
+    </div>
+</div>
+'''
 
 
 # pylint: disable=too-many-instance-attributes
@@ -37,6 +64,7 @@ def __init__(
             url_base_pathname='/',
             compress=True,
             meta_tags=None,
+            index_string=_default_index,
             **kwargs):
 
         # pylint-disable: too-many-instance-attributes
@@ -72,6 +100,7 @@ def __init__(
         # list of dependencies
         self.callback_map = {}
 
+        self.index_string = index_string
         self._meta_tags = meta_tags or []
         self._favicon = None
 
@@ -328,27 +357,17 @@ def index(self, *args, **kwargs):  # pylint: disable=unused-argument
         config = self._generate_config_html()
         metas = self._generate_meta_html()
         title = getattr(self, 'title', 'Dash')
-        return '''
-        <!DOCTYPE html>
-        <html>
-            <head>
-                {}
-                <title>{}</title>
-                {}
-            </head>
-            <body>
-                <div id="react-entry-point">
-                    <div class="_dash-loading">
-                        Loading...
-                    </div>
-                </div>
-                <footer>
-                    {}
-                    {}
-                </footer>
-            </body>
-        </html>
-        '''.format(metas, title, css, config, scripts)
+        return self.interpolate_index(
+            metas, title, css, config, scripts, _app_entry)
+
+    def interpolate_index(self, metas, title, css, config, scripts, app_entry):
+        return interpolate_str(self.index_string,
+                               metas=metas,
+                               title=title,
+                               css=css,
+                               config=config,
+                               scripts=scripts,
+                               app_entry=app_entry)
 
     def dependencies(self):
         return flask.jsonify([

From cd0c15c04eddefc49663ea6d82edd29a02f0bbb9 Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Tue, 10 Jul 2018 15:24:20 -0400
Subject: [PATCH 14/27] Re-add support for favicon in interpolate_index.

---
 dash/dash.py | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/dash/dash.py b/dash/dash.py
index d5d947661a..8ea5575cee 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -30,6 +30,7 @@
     <head>
         %(metas)
         <title>%(title)</title>
+        %(favicon)
         %(css)
     </head>
     <body>
@@ -357,16 +358,22 @@ def index(self, *args, **kwargs):  # pylint: disable=unused-argument
         config = self._generate_config_html()
         metas = self._generate_meta_html()
         title = getattr(self, 'title', 'Dash')
+        favicon = '<link rel="icon" type="image/png" href="{}">'.format(
+            flask.url_for('assets.static', filename=self._favicon))\
+            if self._favicon else ''
         return self.interpolate_index(
-            metas, title, css, config, scripts, _app_entry)
+            metas, title, css, config, scripts, _app_entry, favicon)
 
-    def interpolate_index(self, metas, title, css, config, scripts, app_entry):
+    def interpolate_index(self,
+                          metas, title, css, config,
+                          scripts, app_entry, favicon):
         return interpolate_str(self.index_string,
                                metas=metas,
                                title=title,
                                css=css,
                                config=config,
                                scripts=scripts,
+                               favicon=favicon,
                                app_entry=app_entry)
 
     def dependencies(self):

From 0d9151c636a180bdefe119cd481689ffc52193bb Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Tue, 10 Jul 2018 15:46:32 -0400
Subject: [PATCH 15/27] Change add_meta_tag args to a dict to support every
 meta attributes.

---
 dash/dash.py              |  4 ++--
 tests/test_integration.py | 26 +++++++++-----------------
 2 files changed, 11 insertions(+), 19 deletions(-)

diff --git a/dash/dash.py b/dash/dash.py
index 8ea5575cee..401e156718 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -658,8 +658,8 @@ def add_resource(p):
                 elif f == 'favicon.ico':
                     self._favicon = path
 
-    def add_meta_tag(self, name, content):
-        self._meta_tags.append({'name': name, 'content': content})
+    def add_meta_tag(self, meta):
+        self._meta_tags.append(meta)
 
     def run_server(self,
                    port=8050,
diff --git a/tests/test_integration.py b/tests/test_integration.py
index 25ec3c19da..0dbb131e60 100644
--- a/tests/test_integration.py
+++ b/tests/test_integration.py
@@ -6,6 +6,7 @@
 import dash_core_components as dcc
 import dash_flow_example
 import dash
+
 from dash.dependencies import Input, Output
 from dash.exceptions import PreventUpdate
 from .IntegrationTests import IntegrationTests
@@ -13,13 +14,6 @@
 
 
 class Tests(IntegrationTests):
-    def setUp(self):
-        def wait_for_element_by_id(id):
-            wait_for(lambda: None is not invincible(
-                lambda: self.driver.find_element_by_id(id)
-            ))
-            return self.driver.find_element_by_id(id)
-        self.wait_for_element_by_id = wait_for_element_by_id
 
     def test_simple_callback(self):
         app = dash.Dash(__name__)
@@ -268,22 +262,20 @@ def display_output(react_value, flow_value):
         self.percy_snapshot(name='flowtype')
 
     def test_meta_tags(self):
-        app = dash.Dash()
-
-        app.layout = html.Div(id='content')
-
         metas = (
-            ('description', 'my dash app'),
-            ('custom', 'customized')
+            {'name': 'description', 'content': 'my dash app'},
+            {'name': 'custom', 'content': 'customized'}
         )
 
-        for m in metas:
-            app.add_meta_tag(*m)
+        app = dash.Dash(meta_tags=metas)
+
+        app.layout = html.Div(id='content')
 
         self.startServer(app)
 
         meta = self.driver.find_elements_by_tag_name('meta')
 
+        # -1 for the meta charset.
         self.assertEqual(len(metas), len(meta) - 1, 'Not enough meta tags')
 
         for i in range(1, len(meta)):
@@ -291,5 +283,5 @@ def test_meta_tags(self):
             meta_info = metas[i - 1]
             name = meta_tag.get_attribute('name')
             content = meta_tag.get_attribute('content')
-            self.assertEqual(name, meta_info[0])
-            self.assertEqual(content, meta_info[1])
+            self.assertEqual(name, meta_info['name'])
+            self.assertEqual(content, meta_info['content'])

From ff1cff3e80337e6afcd0d50abba6c947ff98d4bf Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Tue, 10 Jul 2018 16:31:27 -0400
Subject: [PATCH 16/27] Add test for index customization.

---
 dash/_utils.py            |  2 +-
 dash/dash.py              | 45 +++++++++++++++--------------
 tests/test_integration.py | 59 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 84 insertions(+), 22 deletions(-)

diff --git a/dash/_utils.py b/dash/_utils.py
index 11d1cfd6f6..55ea16f72d 100644
--- a/dash/_utils.py
+++ b/dash/_utils.py
@@ -1,7 +1,7 @@
 def interpolate_str(template, **data):
     s = template
     for k, v in data.items():
-        key = '%({})'.format(k)
+        key = '{' + k + '}'
         s = s.replace(key, v)
     return s
 
diff --git a/dash/dash.py b/dash/dash.py
index 401e156718..89d2cc69e3 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -22,22 +22,22 @@
 from .development.base_component import Component
 from . import exceptions
 from ._utils import AttributeDict as _AttributeDict
-from ._utils import interpolate_str
+from ._utils import interpolate_str as _interpolate
 
 _default_index = '''
 <!DOCTYPE html>
 <html>
     <head>
-        %(metas)
-        <title>%(title)</title>
-        %(favicon)
-        %(css)
+        {metas}
+        <title>{title}</title>
+        {favicon}
+        {css}
     </head>
     <body>
-        %(app_entry)
+        {app_entry}
         <footer>
-            %(config)
-            %(scripts)
+            {config}
+            {scripts}
         </footer>
     </body>
 </html>
@@ -59,6 +59,7 @@ def __init__(
             self,
             name='__main__',
             server=None,
+            static_folder='static',
             assets_folder=None,
             assets_url_path='/assets',
             include_assets_files=True,
@@ -84,7 +85,7 @@ def __init__(
         )
 
         # allow users to supply their own flask server
-        self.server = server or Flask(name)
+        self.server = server or Flask(name, static_folder=static_folder)
 
         self.url_base_pathname = url_base_pathname
         self.config = _AttributeDict({
@@ -309,7 +310,7 @@ def _generate_config_html(self):
         ).format(json.dumps(self._config()))
 
     def _generate_meta_html(self):
-        has_charset = any(filter(lambda x: 'charset' in x, self._meta_tags))
+        has_charset = any('charset' in x for x in self._meta_tags)
 
         tags = []
         if not has_charset:
@@ -358,23 +359,25 @@ def index(self, *args, **kwargs):  # pylint: disable=unused-argument
         config = self._generate_config_html()
         metas = self._generate_meta_html()
         title = getattr(self, 'title', 'Dash')
-        favicon = '<link rel="icon" type="image/png" href="{}">'.format(
-            flask.url_for('assets.static', filename=self._favicon))\
-            if self._favicon else ''
+        if self._favicon:
+            favicon = '<link rel="icon" type="image/x-icon" href="{}">'.format(
+                flask.url_for('assets.static', filename=self._favicon))
+        else:
+            favicon = ''
         return self.interpolate_index(
             metas, title, css, config, scripts, _app_entry, favicon)
 
     def interpolate_index(self,
                           metas, title, css, config,
                           scripts, app_entry, favicon):
-        return interpolate_str(self.index_string,
-                               metas=metas,
-                               title=title,
-                               css=css,
-                               config=config,
-                               scripts=scripts,
-                               favicon=favicon,
-                               app_entry=app_entry)
+        return _interpolate(self.index_string,
+                            metas=metas,
+                            title=title,
+                            css=css,
+                            config=config,
+                            scripts=scripts,
+                            favicon=favicon,
+                            app_entry=app_entry)
 
     def dependencies(self):
         return flask.jsonify([
diff --git a/tests/test_integration.py b/tests/test_integration.py
index 0dbb131e60..0641e53c9e 100644
--- a/tests/test_integration.py
+++ b/tests/test_integration.py
@@ -6,6 +6,7 @@
 import dash_core_components as dcc
 import dash_flow_example
 import dash
+import time
 
 from dash.dependencies import Input, Output
 from dash.exceptions import PreventUpdate
@@ -14,6 +15,13 @@
 
 
 class Tests(IntegrationTests):
+    def setUp(self):
+        def wait_for_element_by_id(id):
+            wait_for(lambda: None is not invincible(
+                lambda: self.driver.find_element_by_id(id)
+            ))
+            return self.driver.find_element_by_id(id)
+        self.wait_for_element_by_id = wait_for_element_by_id
 
     def test_simple_callback(self):
         app = dash.Dash(__name__)
@@ -285,3 +293,54 @@ def test_meta_tags(self):
             content = meta_tag.get_attribute('content')
             self.assertEqual(name, meta_info['name'])
             self.assertEqual(content, meta_info['content'])
+
+    def test_index_customization(self):
+        app = dash.Dash()
+
+        app.index_string = '''
+        <!DOCTYPE html>
+        <html>
+            <head>
+                {metas}
+                <title>{title}</title>
+                {favicon}
+                {css}
+            </head>
+            <body>
+                <div id="custom-header">My custom header</div>
+                <div id="add"></div>
+                {app_entry}
+                <footer>
+                    {config}
+                    {scripts}
+                </footer>
+                <div id="custom-footer">My custom footer</div>
+                <script>
+                // Test the formatting doesn't mess up script tags.
+                var elem = document.getElementById('add');
+                if (!elem) {
+                    throw Error('could not find container to add');
+                }
+                elem.innerHTML = 'Got added';
+                </script>
+            </body>
+        </html>
+        '''
+
+        app.layout = html.Div('Dash app', id='app')
+
+        self.startServer(app)
+
+        time.sleep(0.5)
+
+        header = self.wait_for_element_by_id('custom-header')
+        footer = self.wait_for_element_by_id('custom-footer')
+
+        self.assertEqual('My custom header', header.text)
+        self.assertEqual('My custom footer', footer.text)
+
+        add = self.wait_for_element_by_id('add')
+
+        self.assertEqual('Got added', add.text)
+
+        self.percy_snapshot('custom-index')

From eaf91a1fb6d33a0a553e09e6af32ce33b591381a Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Wed, 11 Jul 2018 16:44:47 -0400
Subject: [PATCH 17/27] Add test for assets.

---
 tests/assets/load_first.js            |  1 +
 tests/assets/nested_css/nested.css    |  3 ++
 tests/assets/nested_js/load_after.js  |  1 +
 tests/assets/nested_js/load_after1.js |  2 ++
 tests/assets/reset.css                |  1 +
 tests/test_integration.py             | 49 +++++++++++++++++++++++++++
 6 files changed, 57 insertions(+)
 create mode 100644 tests/assets/load_first.js
 create mode 100644 tests/assets/nested_css/nested.css
 create mode 100644 tests/assets/nested_js/load_after.js
 create mode 100644 tests/assets/nested_js/load_after1.js
 create mode 100644 tests/assets/reset.css

diff --git a/tests/assets/load_first.js b/tests/assets/load_first.js
new file mode 100644
index 0000000000..b68378509e
--- /dev/null
+++ b/tests/assets/load_first.js
@@ -0,0 +1 @@
+window.tested = ['load_first'];
\ No newline at end of file
diff --git a/tests/assets/nested_css/nested.css b/tests/assets/nested_css/nested.css
new file mode 100644
index 0000000000..24ba3d2fa2
--- /dev/null
+++ b/tests/assets/nested_css/nested.css
@@ -0,0 +1,3 @@
+#content {
+    padding: 8px;
+}
\ No newline at end of file
diff --git a/tests/assets/nested_js/load_after.js b/tests/assets/nested_js/load_after.js
new file mode 100644
index 0000000000..6f520fdb85
--- /dev/null
+++ b/tests/assets/nested_js/load_after.js
@@ -0,0 +1 @@
+window.tested.push('load_after');
\ No newline at end of file
diff --git a/tests/assets/nested_js/load_after1.js b/tests/assets/nested_js/load_after1.js
new file mode 100644
index 0000000000..ee2f5b5549
--- /dev/null
+++ b/tests/assets/nested_js/load_after1.js
@@ -0,0 +1,2 @@
+window.tested.push('load_after1');
+document.getElementById('tested').innerHTML = JSON.stringify(window.tested);
diff --git a/tests/assets/reset.css b/tests/assets/reset.css
new file mode 100644
index 0000000000..8c521ddd5e
--- /dev/null
+++ b/tests/assets/reset.css
@@ -0,0 +1 @@
+body {margin: 0;}
diff --git a/tests/test_integration.py b/tests/test_integration.py
index 0641e53c9e..6674497933 100644
--- a/tests/test_integration.py
+++ b/tests/test_integration.py
@@ -1,3 +1,4 @@
+import json
 from multiprocessing import Value
 import datetime
 import itertools
@@ -344,3 +345,51 @@ def test_index_customization(self):
         self.assertEqual('Got added', add.text)
 
         self.percy_snapshot('custom-index')
+
+    def test_assets(self):
+        app = dash.Dash(assets_folder='tests/assets')
+        app.index_string = '''
+        <!DOCTYPE html>
+        <html>
+            <head>
+                {metas}
+                <title>{title}</title>
+                {css}
+            </head>
+            <body>
+                <div id="tested"></div>
+                {app_entry}
+                <footer>
+                    {config}
+                    {scripts}
+                </footer>
+            </body>
+        </html>
+        '''
+
+        app.layout = html.Div([
+            html.Div(id='content'),
+            dcc.Input(id='test')
+        ], id='layout')
+
+        self.startServer(app)
+
+        body = self.driver.find_element_by_tag_name('body')
+
+        body_margin = body.value_of_css_property('margin')
+        self.assertEqual('0px', body_margin)
+
+        content = self.wait_for_element_by_id('content')
+        content_padding = content.value_of_css_property('padding')
+        self.assertEqual('8px', content_padding)
+
+        tested = self.wait_for_element_by_id('tested')
+        tested = json.loads(tested.text)
+        self.assertEqual(3, len(tested))
+
+        order = ('load_first', 'load_after', 'load_after1')
+
+        for i in range(3):
+            self.assertEqual(order[i], tested[i])
+
+        self.percy_snapshot('test assets includes')

From 2197e387d3f4d0c55a7fb203dbe90076d53fbcc8 Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Wed, 11 Jul 2018 18:15:58 -0400
Subject: [PATCH 18/27] Add checks for index, change the format syntax to
 {%key%}, more tests.

---
 dash/_utils.py            |  2 +-
 dash/dash.py              | 66 +++++++++++++++++++++++++++++++++------
 tests/test_integration.py | 65 ++++++++++++++++++++++++++++++--------
 3 files changed, 110 insertions(+), 23 deletions(-)

diff --git a/dash/_utils.py b/dash/_utils.py
index 55ea16f72d..1c6e5ca51c 100644
--- a/dash/_utils.py
+++ b/dash/_utils.py
@@ -1,7 +1,7 @@
 def interpolate_str(template, **data):
     s = template
     for k, v in data.items():
-        key = '{' + k + '}'
+        key = '{%' + k + '%}'
         s = s.replace(key, v)
     return s
 
diff --git a/dash/dash.py b/dash/dash.py
index 89d2cc69e3..80c4e93071 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -28,16 +28,16 @@
 <!DOCTYPE html>
 <html>
     <head>
-        {metas}
-        <title>{title}</title>
-        {favicon}
-        {css}
+        {%metas%}
+        <title>{%title%}</title>
+        {%favicon%}
+        {%css%}
     </head>
     <body>
-        {app_entry}
+        {%app_entry%}
         <footer>
-            {config}
-            {scripts}
+            {%config%}
+            {%scripts%}
         </footer>
     </body>
 </html>
@@ -51,9 +51,17 @@
 </div>
 '''
 
+_re_index_entry = re.compile(r'{%app_entry%}')
+_re_index_config = re.compile(r'{%config%}')
+_re_index_scripts = re.compile(r'{%scripts%}')
+
+_re_index_entry_id = re.compile(r'(id="react-entry-point")')
+_re_index_config_id = re.compile(r'(id="_dash-config")')
+_re_index_scripts_id = re.compile(r'(src=".*dash[-_]renderer.*")')
+
 
 # pylint: disable=too-many-instance-attributes
-# pylint: disable=too-many-arguments, too-many-locals
+# pylint: disable=too-many-arguments
 class Dash(object):
     def __init__(
             self,
@@ -102,6 +110,7 @@ def __init__(
         # list of dependencies
         self.callback_map = {}
 
+        self._index_string = ''
         self.index_string = index_string
         self._meta_tags = meta_tags or []
         self._favicon = None
@@ -200,6 +209,26 @@ def layout(self, value):
         self.css._update_layout(layout_value)
         self.scripts._update_layout(layout_value)
 
+    @property
+    def index_string(self):
+        return self._index_string
+
+    @index_string.setter
+    def index_string(self, value):
+        checks = (
+            (_re_index_entry.search(value), 'app_entry'),
+            (_re_index_config.search(value), 'config',),
+            (_re_index_scripts.search(value), 'scripts'),
+        )
+        missing = [missing for check, missing in checks if not check]
+        if missing:
+            raise Exception(
+                'Did you forget to include {} in your index string ?'.format(
+                    ', '.join('{%' + x + '%}' for x in missing)
+                )
+            )
+        self._index_string = value
+
     def serve_layout(self):
         layout = self._layout_value()
 
@@ -364,9 +393,28 @@ def index(self, *args, **kwargs):  # pylint: disable=unused-argument
                 flask.url_for('assets.static', filename=self._favicon))
         else:
             favicon = ''
-        return self.interpolate_index(
+
+        index = self.interpolate_index(
             metas, title, css, config, scripts, _app_entry, favicon)
 
+        checks = (
+            (_re_index_entry_id.search(index), '#react-entry-point'),
+            (_re_index_config_id.search(index), '#_dash-configs'),
+            (_re_index_scripts_id.search(index), 'dash-renderer'),
+        )
+        missing = [missing for check, missing in checks if not check]
+
+        if missing:
+            plural = 's' if len(missing) > 1 else ''
+            raise Exception(
+                'Missing element{pl} {ids} in index.'.format(
+                    ids=', '.join(missing),
+                    pl=plural
+                )
+            )
+
+        return index
+
     def interpolate_index(self,
                           metas, title, css, config,
                           scripts, app_entry, favicon):
diff --git a/tests/test_integration.py b/tests/test_integration.py
index 6674497933..d333a9e469 100644
--- a/tests/test_integration.py
+++ b/tests/test_integration.py
@@ -6,6 +6,7 @@
 import dash_html_components as html
 import dash_core_components as dcc
 import dash_flow_example
+
 import dash
 import time
 
@@ -302,18 +303,18 @@ def test_index_customization(self):
         <!DOCTYPE html>
         <html>
             <head>
-                {metas}
-                <title>{title}</title>
-                {favicon}
-                {css}
+                {%metas%}
+                <title>{%title%}</title>
+                {%favicon%}
+                {%css%}
             </head>
             <body>
                 <div id="custom-header">My custom header</div>
                 <div id="add"></div>
-                {app_entry}
+                {%app_entry%}
                 <footer>
-                    {config}
-                    {scripts}
+                    {%config%}
+                    {%scripts%}
                 </footer>
                 <div id="custom-footer">My custom footer</div>
                 <script>
@@ -323,6 +324,9 @@ def test_index_customization(self):
                     throw Error('could not find container to add');
                 }
                 elem.innerHTML = 'Got added';
+                var config = {};
+                fetch('/nonexist').then(r => r.json())
+                    .then(r => config = r).catch(err => ({config}));
                 </script>
             </body>
         </html>
@@ -352,16 +356,16 @@ def test_assets(self):
         <!DOCTYPE html>
         <html>
             <head>
-                {metas}
-                <title>{title}</title>
-                {css}
+                {%metas%}
+                <title>{%title%}</title>
+                {%css%}
             </head>
             <body>
                 <div id="tested"></div>
-                {app_entry}
+                {%app_entry%}
                 <footer>
-                    {config}
-                    {scripts}
+                    {%config%}
+                    {%scripts%}
                 </footer>
             </body>
         </html>
@@ -393,3 +397,38 @@ def test_assets(self):
             self.assertEqual(order[i], tested[i])
 
         self.percy_snapshot('test assets includes')
+
+    def test_invalid_index_string(self):
+        app = dash.Dash()
+
+        def will_raise():
+            app.index_string = '''
+                    <!DOCTYPE html>
+                    <html>
+                        <head>
+                            {%metas%}
+                            <title>{%title%}</title>
+                            {%favicon%}
+                            {%css%}
+                        </head>
+                        <body>
+                            <div id="custom-header">My custom header</div>
+                            <div id="add"></div>
+                            <footer>
+                            </footer>
+                        </body>
+                    </html>
+                    '''
+
+        with self.assertRaises(Exception) as context:
+            will_raise()
+
+        app.layout = html.Div()
+        self.startServer(app)
+
+        exc_msg = str(context.exception)
+        self.assertTrue('{%app_entry%}' in exc_msg)
+        self.assertTrue('{%config%}' in exc_msg)
+        self.assertTrue('{%scripts%}' in exc_msg)
+        time.sleep(0.5)
+        print('invalid index string')

From ea0d2ca5fd87f377927f7a35b16c00de511575be Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Tue, 17 Jul 2018 16:11:46 -0400
Subject: [PATCH 19/27] Change interpolate_index params to kwargs.

---
 dash/dash.py | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/dash/dash.py b/dash/dash.py
index 80c4e93071..9866cb77dd 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -55,9 +55,9 @@
 _re_index_config = re.compile(r'{%config%}')
 _re_index_scripts = re.compile(r'{%scripts%}')
 
-_re_index_entry_id = re.compile(r'(id="react-entry-point")')
-_re_index_config_id = re.compile(r'(id="_dash-config")')
-_re_index_scripts_id = re.compile(r'(src=".*dash[-_]renderer.*")')
+_re_index_entry_id = re.compile(r'id="react-entry-point"')
+_re_index_config_id = re.compile(r'id="_dash-config"')
+_re_index_scripts_id = re.compile(r'src=".*dash[-_]renderer.*"')
 
 
 # pylint: disable=too-many-instance-attributes
@@ -101,8 +101,7 @@ def __init__(
             'routes_pathname_prefix': url_base_pathname,
             'requests_pathname_prefix': url_base_pathname,
             'include_assets_files': include_assets_files,
-            'assets_folder': assets_folder or os.path.join(
-                os.getcwd(), 'assets'),
+            'assets_folder': self.assets_folder,
             'assets_external_path': '',
             'assets_url_path': assets_url_path,
         })
@@ -395,7 +394,8 @@ def index(self, *args, **kwargs):  # pylint: disable=unused-argument
             favicon = ''
 
         index = self.interpolate_index(
-            metas, title, css, config, scripts, _app_entry, favicon)
+            metas=metas, title=title, css=css, config=config,
+            scripts=scripts, app_entry=_app_entry, favicon=favicon)
 
         checks = (
             (_re_index_entry_id.search(index), '#react-entry-point'),
@@ -416,8 +416,8 @@ def index(self, *args, **kwargs):  # pylint: disable=unused-argument
         return index
 
     def interpolate_index(self,
-                          metas, title, css, config,
-                          scripts, app_entry, favicon):
+                          metas='', title='', css='', config='',
+                          scripts='', app_entry='', favicon=''):
         return _interpolate(self.index_string,
                             metas=metas,
                             title=title,

From 4cf9e5ca2683c4d282ccdb6b6f5f2e7c5454ad38 Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Tue, 17 Jul 2018 16:22:51 -0400
Subject: [PATCH 20/27] Remove `add_meta_tag`.

---
 dash/dash.py | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/dash/dash.py b/dash/dash.py
index 9866cb77dd..cb191cb7c3 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -709,9 +709,6 @@ def add_resource(p):
                 elif f == 'favicon.ico':
                     self._favicon = path
 
-    def add_meta_tag(self, meta):
-        self._meta_tags.append(meta)
-
     def run_server(self,
                    port=8050,
                    debug=False,

From f6e9922e37e596d1043abfe62be110165d4135a1 Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Wed, 18 Jul 2018 10:45:07 -0400
Subject: [PATCH 21/27] Block pylint version to 1.9.2

---
 dev-requirements.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/dev-requirements.txt b/dev-requirements.txt
index 282b362edc..f667e354c3 100644
--- a/dev-requirements.txt
+++ b/dev-requirements.txt
@@ -12,4 +12,4 @@ six
 plotly>=2.0.8
 requests[security]
 flake8
-pylint
+pylint==1.9.2

From 8cc781bb0c21c6f9f7a94b80c1edb3f8b18b87f4 Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Mon, 23 Jul 2018 17:37:14 -0400
Subject: [PATCH 22/27] Put assets Blueprint in ctor, remove related configs.

---
 dash/dash.py | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/dash/dash.py b/dash/dash.py
index cb191cb7c3..951a6a8c30 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -86,24 +86,25 @@ def __init__(
                 See https://github.com/plotly/dash/issues/141 for details.
                 ''', DeprecationWarning)
 
-        name = name or 'dash'
-
-        self.assets_folder = assets_folder or os.path.join(
+        self._assets_folder = assets_folder or os.path.join(
             os.getcwd(), 'assets'
         )
 
         # allow users to supply their own flask server
         self.server = server or Flask(name, static_folder=static_folder)
 
+        self.server.register_blueprint(
+            flask.Blueprint('assets', 'assets',
+                            static_folder=self._assets_folder,
+                            static_url_path=assets_url_path))
+
         self.url_base_pathname = url_base_pathname
         self.config = _AttributeDict({
             'suppress_callback_exceptions': False,
             'routes_pathname_prefix': url_base_pathname,
             'requests_pathname_prefix': url_base_pathname,
             'include_assets_files': include_assets_files,
-            'assets_folder': self.assets_folder,
             'assets_external_path': '',
-            'assets_url_path': assets_url_path,
         })
 
         # list of dependencies
@@ -675,7 +676,7 @@ def _setup_server(self):
         self._generate_css_dist_html()
 
     def _walk_assets_directory(self):
-        walk_dir = self.config.assets_folder
+        walk_dir = self._assets_folder
         slash_splitter = re.compile(r'[\\/]+')
 
         def add_resource(p):
@@ -713,8 +714,4 @@ def run_server(self,
                    port=8050,
                    debug=False,
                    **flask_run_options):
-        bp = flask.Blueprint('assets', 'assets',
-                             static_folder=self.config.assets_folder,
-                             static_url_path=self.config.assets_url_path)
-        self.server.register_blueprint(bp)
         self.server.run(port=port, debug=debug, **flask_run_options)

From 0046402b18ea07cce0954c0c3ce1e61ceecca0bc Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Mon, 23 Jul 2018 18:00:23 -0400
Subject: [PATCH 23/27] Use `flask.helpers.get_root_path` for assets folder
 resolution.

---
 dash/dash.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/dash/dash.py b/dash/dash.py
index 951a6a8c30..9e39356036 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -87,7 +87,7 @@ def __init__(
                 ''', DeprecationWarning)
 
         self._assets_folder = assets_folder or os.path.join(
-            os.getcwd(), 'assets'
+            flask.helpers.get_root_path(name), 'assets'
         )
 
         # allow users to supply their own flask server

From 6af0381a72388647ba3245a03a98d2e46e536e5b Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Tue, 24 Jul 2018 10:55:00 -0400
Subject: [PATCH 24/27] Add docstring to interpolate_index.

---
 dash/dash.py | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/dash/dash.py b/dash/dash.py
index 9e39356036..8aeb569ad6 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -419,6 +419,42 @@ def index(self, *args, **kwargs):  # pylint: disable=unused-argument
     def interpolate_index(self,
                           metas='', title='', css='', config='',
                           scripts='', app_entry='', favicon=''):
+        """
+        Called to create the initial HTML string that is loaded on page.
+        Override this method to provide you own custom HTML.
+
+        :Example:
+
+            class MyDash(dash.Dash):
+                def interpolate_index(self, **kwargs):
+                    return '''
+                    <!DOCTYPE html>
+                    <html>
+                        <head>
+                            <title>My App</title>
+                        </head>
+                        <body>
+                            <div id="custom-header">My custom header</div>
+                            {}
+                            {}
+                            {}
+                            <div id="custom-footer">My custom footer</div>
+                        </body>
+                    </html>
+                    '''.format(
+                        kwargs.get('app_entry'),
+                        kwargs.get('config'),
+                        kwargs.get('scripts'))
+
+        :param metas: Collected & formatted meta tags.
+        :param title: The title of the app.
+        :param css: Collected & formatted css dependencies as <link> tags.
+        :param config: Configs needed by dash-renderer.
+        :param scripts: Collected & formatted scripts tags.
+        :param app_entry: Where the app will render.
+        :param favicon: A favicon <link> tag if found in assets folder.
+        :return: The interpolated HTML string for the index.
+        """
         return _interpolate(self.index_string,
                             metas=metas,
                             title=title,

From 2c104a54a1418d7708ec803813e78aba07c90fa8 Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Wed, 25 Jul 2018 11:02:33 -0400
Subject: [PATCH 25/27] Ensure assets files are ordered, add more test files.

---
 dash/dash.py                           | 14 +++++++-------
 tests/assets/nested_js/load_after1.js  |  1 -
 tests/assets/nested_js/load_after10.js |  1 +
 tests/assets/nested_js/load_after11.js |  1 +
 tests/assets/nested_js/load_after2.js  |  1 +
 tests/assets/nested_js/load_after3.js  |  1 +
 tests/assets/nested_js/load_after4.js  |  1 +
 tests/assets/nested_js/load_last.js    |  1 +
 tests/test_integration.py              |  9 ++++++---
 9 files changed, 19 insertions(+), 11 deletions(-)
 create mode 100644 tests/assets/nested_js/load_after10.js
 create mode 100644 tests/assets/nested_js/load_after11.js
 create mode 100644 tests/assets/nested_js/load_after2.js
 create mode 100644 tests/assets/nested_js/load_after3.js
 create mode 100644 tests/assets/nested_js/load_after4.js
 create mode 100644 tests/assets/nested_js/load_last.js

diff --git a/dash/dash.py b/dash/dash.py
index 8aeb569ad6..edc3ccc2bb 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -435,16 +435,16 @@ def interpolate_index(self, **kwargs):
                         </head>
                         <body>
                             <div id="custom-header">My custom header</div>
-                            {}
-                            {}
-                            {}
+                            {app_entry}
+                            {config}
+                            {scripts}
                             <div id="custom-footer">My custom footer</div>
                         </body>
                     </html>
                     '''.format(
-                        kwargs.get('app_entry'),
-                        kwargs.get('config'),
-                        kwargs.get('scripts'))
+                        app_entry=kwargs.get('app_entry'),
+                        config=kwargs.get('config'),
+                        scripts=kwargs.get('scripts'))
 
         :param metas: Collected & formatted meta tags.
         :param title: The title of the app.
@@ -733,7 +733,7 @@ def add_resource(p):
                 else:
                     base = splitted[0]
 
-            for f in files:
+            for f in sorted(files):
                 if base:
                     path = '/'.join([base, f])
                 else:
diff --git a/tests/assets/nested_js/load_after1.js b/tests/assets/nested_js/load_after1.js
index ee2f5b5549..1629d393d7 100644
--- a/tests/assets/nested_js/load_after1.js
+++ b/tests/assets/nested_js/load_after1.js
@@ -1,2 +1 @@
 window.tested.push('load_after1');
-document.getElementById('tested').innerHTML = JSON.stringify(window.tested);
diff --git a/tests/assets/nested_js/load_after10.js b/tests/assets/nested_js/load_after10.js
new file mode 100644
index 0000000000..fcfdb59ae9
--- /dev/null
+++ b/tests/assets/nested_js/load_after10.js
@@ -0,0 +1 @@
+window.tested.push('load_after10');
\ No newline at end of file
diff --git a/tests/assets/nested_js/load_after11.js b/tests/assets/nested_js/load_after11.js
new file mode 100644
index 0000000000..bd11cd28be
--- /dev/null
+++ b/tests/assets/nested_js/load_after11.js
@@ -0,0 +1 @@
+window.tested.push('load_after11');
\ No newline at end of file
diff --git a/tests/assets/nested_js/load_after2.js b/tests/assets/nested_js/load_after2.js
new file mode 100644
index 0000000000..0b76a55fae
--- /dev/null
+++ b/tests/assets/nested_js/load_after2.js
@@ -0,0 +1 @@
+window.tested.push('load_after2');
\ No newline at end of file
diff --git a/tests/assets/nested_js/load_after3.js b/tests/assets/nested_js/load_after3.js
new file mode 100644
index 0000000000..d913af94e7
--- /dev/null
+++ b/tests/assets/nested_js/load_after3.js
@@ -0,0 +1 @@
+window.tested.push('load_after3');
\ No newline at end of file
diff --git a/tests/assets/nested_js/load_after4.js b/tests/assets/nested_js/load_after4.js
new file mode 100644
index 0000000000..2507e38b00
--- /dev/null
+++ b/tests/assets/nested_js/load_after4.js
@@ -0,0 +1 @@
+window.tested.push('load_after4');
\ No newline at end of file
diff --git a/tests/assets/nested_js/load_last.js b/tests/assets/nested_js/load_last.js
new file mode 100644
index 0000000000..285aa60506
--- /dev/null
+++ b/tests/assets/nested_js/load_last.js
@@ -0,0 +1 @@
+document.getElementById('tested').innerHTML = JSON.stringify(window.tested);
diff --git a/tests/test_integration.py b/tests/test_integration.py
index d333a9e469..770b9152cb 100644
--- a/tests/test_integration.py
+++ b/tests/test_integration.py
@@ -389,11 +389,14 @@ def test_assets(self):
 
         tested = self.wait_for_element_by_id('tested')
         tested = json.loads(tested.text)
-        self.assertEqual(3, len(tested))
 
-        order = ('load_first', 'load_after', 'load_after1')
+        order = ('load_first', 'load_after', 'load_after1',
+                 'load_after10', 'load_after11', 'load_after2',
+                 'load_after3', 'load_after4', )
 
-        for i in range(3):
+        self.assertEqual(len(order), len(tested))
+
+        for i in range(len(tested)):
             self.assertEqual(order[i], tested[i])
 
         self.percy_snapshot('test assets includes')

From 1171f0adfeee9950ec18a34a9fc494cdf392793c Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Wed, 25 Jul 2018 12:18:31 -0400
Subject: [PATCH 26/27] Update changelog and version.

---
 CHANGELOG.md    | 5 +++++
 dash/version.py | 2 +-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3455701ca7..da263773ca 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,8 @@
+## 0.22.0 - 2018-07-25
+## Added
+- Assets files & index customization [#286](https://github.com/plotly/dash/pull/286)
+- Raise an error if there is no layout present when the server is running [#294](https://github.com/plotly/dash/pull/294)
+
 ## 0.21.1 - 2018-04-10
 ## Added
 - `aria-*` and `data-*` attributes are now supported in all dash html components. (#40)
diff --git a/dash/version.py b/dash/version.py
index 8c306aa668..81edede8b4 100644
--- a/dash/version.py
+++ b/dash/version.py
@@ -1 +1 @@
-__version__ = '0.21.1'
+__version__ = '0.22.0'

From 495762ee782fa64706212fe3e0a97bd1f61879ea Mon Sep 17 00:00:00 2001
From: Philippe Duval <philippe@plot.ly>
Date: Wed, 25 Jul 2018 12:37:56 -0400
Subject: [PATCH 27/27] pylint fixes.

---
 dash/dash.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/dash/dash.py b/dash/dash.py
index 7399e83501..44fad1efee 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -707,7 +707,7 @@ def dispatch(self):
     def _setup_server(self):
         if self.config.include_assets_files:
             self._walk_assets_directory()
-      
+
         # Make sure `layout` is set before running the server
         value = getattr(self, 'layout')
         if value is None:
@@ -717,7 +717,7 @@ def _setup_server(self):
                 'at the time that `run_server` was called. '
                 'Make sure to set the `layout` attribute of your application '
                 'before running the server.')
-            
+
         self._generate_scripts_html()
         self._generate_css_dist_html()